Subtopic: Measurement of force, stress, torque, speed, displacement and acceleration on machine elements – shafts, couplings, keys, bearings and knuckle joints
Question Statement:
Which of the following statements regarding mechanical shaft couplings used in agricultural machinery is/are correct?
Options:
(A) An Oldham coupling accommodates lateral (radial) offset between two parallel shafts.
(B) A single Universal (Hooke's) joint operating at a non-zero joint angle causes periodic angular velocity fluctuations in the driven shaft.
(C) Using two universal joints with identical joint angles and in-phase yokes eliminates angular velocity fluctuations between driving and driven shafts.
(D) A rigid sleeve coupling accommodates angular misalignment up to $15^\circ$ without inducing bending stresses.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
• Oldham couplings use a central floating disc with perpendicular tongues to handle parallel radial offsets (A is correct).
• A single Cardan/Hooke's joint has non-uniform output speed $\omega_2 = \omega_1 \frac{\cos\alpha}{1 - \sin^2\alpha \sin^2\theta}$ (B is correct).
• A double Cardan drive with equal angles $\alpha_1 = \alpha_2$ and coplanar yokes cancels out angular speed variations (C is correct).
• Rigid couplings require precise coaxial shaft alignment; any misalignment induces severe fatigue bending stresses (D is false).